This invention relates to adjustable power supply voltage sag generators and ground supply voltage bounce generators for testing the effects of positive power supply sag and ground power supply bounce on integrated circuit performance.
If an integrated circuit contains a significant number of digital circuit devices that switch simultaneously, the value of the ground power supply voltage may rise (bounce) and the value of the positive power supply voltage may drop (sag) momentarily at the time of switching. Power supply sag and bounce may be significant enough to affect the performance of devices in the integrated circuit.
When designing an integrated circuit, it may be desirable to test the functionality of portions of the integrated circuit before they are incorporated into the complete design. Testing may save time and cost by exposing design issues early on in the development cycle. In particular, it may be desirable to test how a circuit block would perform if it were incorporated into an integrated circuit that suffers from power supply bounce and sag resulting from simultaneous switching effects.
Programmable logic device manufacturers sometimes program integrated circuits so that a particular circuit block of interest is surrounded with numerous devices that switch simultaneously. The manufacturer may then measure the performance of the circuit block under these high-stress conditions. However, this testing technique does not deliver quantifiable and easily tunable power supply sags and bounces to the circuit block and relies on the availability of programmable circuit resources in the vicinity of the circuit block of interest. Attempts to avoid the need to perform this type of test measurement using simulations have proven difficult, because the required computations are complex and involve long run times.
Nevertheless, as semiconductor technology advances, integrated circuits are increasingly being powered with lower positive power supply voltages. This may make it more likely for integrated circuits to suffer from power supply sag and bounce issues if they are not carefully designed. Testing the effects of power supply sag and bounce on integrated circuits during the design process is therefore of growing importance.